Conventionally, there have been air conditioners in which the AMI communication method is used as a signal transmission method between an outdoor unit and an indoor unit.
In the AMI communication method, data items are transmitted according to the predetermined polarity of a signal. If the polarities between the input and output units are not matched with each other due to misconnection or the like, this produces a problem that the contents of data cannot be correctly read out.
For example, if an A unit and a B unit which are connected through a communication line have opposite polarities, when both the units transmit data at the same time, data signals from both the units superpose and cancel each other in the communication line. This reduces the voltage level of the communication line to 0, thereby eliminating data signals.
For this reason, in a conventional transmission device for an air conditioner as disclosed in Japanese Patent Application Laid-Open Gazette No.1-288133, a remote control is connected to a driver and a receiver through an analog switch. When an input signal has a different polarity, ports of the driver and the receiver are switched to other ports so that the transmitting output and the receiving input are matched in polarity with each other.
However, in the above-mentioned transmission device for the air conditioner, determination about the match or mismatch between the polarities is made according to whether the data signal has a designated format. This produces a problem that it is not possible to determine the match or mismatch between the polarities unless a data signal is transmitted by an indoor control unit or the like.
To solve the problem, for example, there has been an air conditioner wherein a DC power source is connected to the communication line to apply a DC voltage thereto and each unit is provided with a transmission circuit, a reception circuit and a polarity discriminating circuit for discriminating the polarity of the communication line, whereby all the units are matched in polarity with each other.
Problems That the Invention is to Solve
In the above-mentioned air conditioner, for commonality of components, each of the indoor units and the outdoor units is provided with a power superposition circuit having a DC power source for polarity discrimination and a discharge resistor for discharging a residual charge in the communication line. The power superposition circuit of any one of the outdoor units and the indoor units applies a DC voltage to the communication line and the discharge resistor is connected to the communication line.
However, if the setting that connects the power superposition circuit of either one of the indoor units and the outdoor units to the communication line is manually made, this requires an address setting. In addition, a problem may occur that two power superposition circuits of two outdoor units are connected to the communication line nevertheless it is essential only that a single power superposition circuit is connected to the communication line. Further, there may be another problem of producing an improper setting wherein the power superposition circuit is not connected to the communication line.
Furthermore, recently, there have been cases that an air conditioner which has a plurality of outdoor units to form a plurality of refrigerant circuits is installed and data transmission is made through a single communication line which connects the plurality of outdoor units and the indoor units.
In this case, it is preferable that the above-mentioned power superposition circuit is provided in each outdoor unit for commonality of outdoor units and the like. If the setting that either one of the power superposition circuits of the outdoor units should be connected to the communication line is manually made, this may produce an improper setting that two power superposition circuits of two outdoor units are connected to the communication line.
For this reason, it can be considered to automatically set the outdoor unit whose power superposition circuit should be connected to the communication line. If only the automatic setting is made, this requires much time every time for the setting. In detail, if one outdoor unit whose power superposition circuit is connected to the communication line is determined and thereafter another outdoor unit is connected to the communication line, an automatic setting operation must be made again. This produces a problem that it takes much time to start air conditioning operation.
This invention has been made in view of the forgoing problems and has its object of readily and securely establishing connection of the power superposition means thereby allowing the polarity of the communication line to be discriminated.
Another object of this invention is to reduce the time for determination of a thermal-source-side control unit for making power superposition, thereby promptly activating air conditioning operation.